Image processing of a portion of multiple patches of a colorbar

ABSTRACT

An image processing apparatus for use with a printed substrate is disclosed. The image processing apparatus comprises an imaging device configured to receive light reflected from a portion of multiple patches of a colorbar on the printed substrate and configured to process color data from the light reflected from the portion of multiple patches of the colorbar.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation-in-part of prior application Ser. No.10/424,230, filed Apr. 25, 2003 and a continuation-in-part of priorapplication Ser. No. 10/790,451, filed Feb. 17, 2004, both of which areincorporated herein by reference in their entireties.

BACKGROUND

The present disclosure relates to an apparatus for measuring spectraland spatial information on a printing press.

In the printing industry, a desired image is repeatedly printed on acontinuous web or substrate such as paper. In a typical printingprocess, the continuous web is slit in the longitudinal direction (thedirection of web movement) to produce a plurality of continuous ribbons.The ribbons are aligned one on top of the other, folded longitudinally,and then cut laterally to produce a plurality of multi-page,approximately page-length segments, each of which is termed a“signature”. The term signature also encompasses a single printed sheetthat has or has not been folded.

To monitor the print quality on a signature, various methods may be usedto measure the color quality of the printed signature. One methodincludes printing a colorbar having multiple color patches of differentknown colors and intensities such that the color quality of the colorbarcan be measured and compared to a standard, the colorbar beingrepresentative of the color quality of the printed signature. By sodoing, the color quality of the printed signature may be measured byutilizing an image processing apparatus (e.g., a camera) to acquire animage of a single point of the printed colorbar. Current imageprocessing apparatus systems for measuring the color quality may utilizea single camera, such as a charge-coupled device (“CCD”) color camerahaving red, green, and blue channels (i.e., an RGB camera).

It may also be desired to provide an image processing device that cantake color measurements at a high rate of speed. The ability to takecolor measurements at a high rate of speed would allow for more directmeasurement of the printed image (i.e., the ability to measure color inthe work in addition to the colorbar), would make the control systemrespond faster to color errors, and would assist in locating a desiredplace on the signature with a searching algorithm for additionalmeasurements.

SUMMARY

One embodiment relates to an image processing apparatus for use with aprinted substrate. The image processing apparatus comprises an imagingdevice configured to receive light reflected from a portion of multiplepatches of a colorbar on the printed substrate and configured to processcolor data from the light reflected from the portion of multiple patchesof the colorbar.

Another embodiment relates to an image processing apparatus for use witha printed substrate. The image processing apparatus comprises an imagingdevice configured to receive light reflected from a slice of multiplepatches of a colorbar on the printed substrate and configured to processcolor data from the light reflected from the slice of multiple patchesof the colorbar.

Other features and advantages of the disclosure will become apparent tothose skilled in the art upon review of the following detaileddescription, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a printing system;

FIG. 2 illustrates an image processing apparatus assembly and a printedimage within the field of view;

FIG. 3 is a schematic diagram of an image processing apparatus assembly,according to an exemplary embodiment;

FIG. 4 is a more detailed schematic of the diagram of FIG. 3, accordingto an exemplary embodiment;

FIG. 5 illustrates the captured image taken through the colorbar patchesof a printed image, according to an exemplary embodiment;

FIG. 6 is a flow chart of a scattered light correction process,according to an exemplary embodiment;

FIG. 7 is a schematic diagram of the optics of the image processingapparatus, according to an exemplary embodiment;

FIG. 8 is a more detailed schematic of the diagram of FIG. 7, accordingto an exemplary embodiment;

FIG. 9 is a schematic diagram of the optics of the image processingapparatus, according to an exemplary embodiment;

FIG. 10 is a schematic diagram of the optics of the image processingapparatus, according to an exemplary embodiment;

FIG. 11 is a schematic diagram of the optics of the image processingapparatus, according to an exemplary embodiment;

FIGS. 12A-12C illustrate detecting a colorbar and focusing light ontothe colorbar, according to an exemplary embodiment;

FIG. 13 is an illustration of acquiring a portion of multiple patchesalong the colorbar, according to an exemplary embodiment;

FIGS. 14A-14C are illustrations of a spatial imaging device and aspectral imaging device acquiring image data from a printed image,according to exemplary embodiments;

FIGS. 15A-15B are block diagrams of a first imaging unit and a secondimaging unit, according to exemplary embodiments;

FIG. 16 is a flowchart for calibrating a spatial imaging device based oncalibration data from a spectral imaging device, according to anexemplary embodiment; and

FIG. 17 is a flowchart for controlling color in a printing operation andreporting out data including color space data and density data,according to an exemplary embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, a printing system 10 for printing a multi-colorimage upon a web 12 is illustrated. In the illustrated embodiment, fourprinting units 14, 16, 18, and 20 each print one color of the image uponweb 12. This type of printing is commonly referred to as web offsetprinting. Each printing unit 14, 16, 18, 20 may include an upper blanketcylinder 22, an upper printing plate cylinder 24, a lower blanketcylinder 26, and a lower printing plate cylinder 28. In printing system10, colors 1, 2, 3, and 4 on printing units 14, 16, 18, and 20respectively, may be black (K), cyan (C), magenta (M), and yellow (Y).However, it is understood that any colors of ink may be effectivelyanalyzed by the present disclosure. The location of printing units 14,16, 18, and 20 relative to each other is determined by the printer, andmay vary.

In the illustrated embodiment, printing system 10 is a web offset press.It is contemplated, however, that the present disclosure may beapplicable to other types of printing systems 10, such as rotogravure,flexographic, and sheet-fed presses. The present disclosure may also beused for other applications, such as for use in the packaging industry.

Printing system 10 may include an image processing apparatus 36 inoptical communication with web 12. Image processing apparatus 36 mayinclude an illumination system 38 and an image recording device 40. Thespecific configuration of image processing apparatus 36 will bedescribed in more detail below. Printing system 10 may include a camerapositioning unit 34, a computer 32, and a web stabilizer 39.

In the printing industry, a printer may print one or more colorbarsalong an edge portion of web 12. Colorbars may include multiple patchesof different colors (K, C, M, and Y), intensities, and half-tone values(such as 25% patches, 50% patches, and 75% patches). Image processingapparatus 36 may capture an image of these colorbars to monitor thecolor quality of web 12. However, it is understood that in someapplications, the colorbars may not be necessary as measurements may betaken from any region within the printed region. The informationobtained from the colorbars or from any other position on web 12 will bedescribed in more detail below.

In general operation, camera positioning unit 34 may move imageprocessing apparatus 36 to a first position on web 12. A printed imagemay be illuminated by illumination system 38 and image recording device40 may record an image signal which is representative of a portion ofthe printed substrate within field of view 56. Illumination system 38may be synchronized with the movement of web 12 such that the recordedimage signal includes a portion of the colorbars. Illumination system 38may be a strobed light, a non-strobed light, an AC light source, a DClight source, or a light-emitting diode (“LED”).

Computer 32 may include random access memory 33 (semiconductor memoryand/or disk drive storage) and an image capture circuitry 48 whichinterfaces with image processing apparatus 36. In other embodiments,computer 32 may be a microprocessor housed within image processingapparatus 36.

Computer 32 may be connected to camera positioning unit 34 by acommunication link 54, and computer 32 may send control signals tocamera positioning unit 34. Camera positioning unit 34 may bemechanically coupled to image processing apparatus 36 and may move imageprocessing apparatus 36 in a direction perpendicular to web 12 motion,termed the lateral direction (X-axis, see FIG. 2). Moving imageprocessing apparatus 36 across web 12 may allow for selective imagerecording of lateral portions of the printed image on web 12. Imageprocessing apparatus 36 may record the printed image within field ofview 56 for various positions of image processing apparatus 36 acrossweb 12. Web 12 may be moving in the Y direction so that circumferentialor Y-axis positioning by camera positioning unit 34 may not be necessarybecause the timing of the strobe light in illumination system 38effectively provides circumferential positioning relative to moving web12, as is further explained below.

It is also contemplated that a positioning unit may not be utilized, if,for example, a plurality of image processing apparatus 36 are combinedto obtain a field of view that covers all required areas of web 12, orif only one area of web 12 is to be monitored. In an exemplaryembodiment, one image processing apparatus 36 may be used to acquiredata across substantially or all of web 12. In other exemplaryembodiments, at least two image processing apparatus 36, at least threeimage processing apparatus 36, at least four image processing apparatus36, etc. may be used to acquire data across substantially or all of web12. In an exemplary embodiment, an overlap between a first imageprocessing apparatus and a second image processing apparatus may beutilized. The overlap may be at least 0.1 inch, at least 0.5 inch, atleast one inch, or any other distance. In another exemplary embodiment,no overlap may be utilized.

Stabilization may be necessary to reduce web 12 motion toward and awayfrom image processing apparatus 36. This motion is termed web flutter.Web flutter may cause the image to sometimes be out of focus and maycause the magnification of the image to change. Web stabilizer 39 may beany mechanism that dampens the flutter of web 12 to within acceptablelimits of depth-of-field for recording the printed image on web 12 byimage processing apparatus 36, without causing the ink to smear. Webstabilizer 39 may be a non-invasive web stabilizer such as thatdisclosed in U.S. Pat. No. 4,913,049 entitled “Bernoulli Effect WebStabilizer.” A non-invasive stabilizer is one that does not makephysical contact with web 12.

Reduction of rippling or corrugations in web 12 may also be necessary.Any ripples in web 12 can cause light and dark spots in the imageobtained from web 12. These light and dark spots do not usually affectthe determination of the location of the colorbar (or whatever otherarea of web 12 that is desired to be imaged), but they may adverselyaffect the color measurements of the image. One way to reduce theseripples in web 12 is to run web 12 over an idler, giving more support toweb 12.

If web 12 is transparent or translucent, accurate optical densitymeasurements may require that light reflected back through web 12 beminimized. This may be accomplished by providing a black backing behindweb 12, providing a large open cavity behind web 12 such that littlelight will be reflected through web 12, or utilizing a black roller ifweb 12 is stabilized by imaging on a roller.

Image processing apparatus 36 and camera positioning unit 34 may bemounted on printing system 10 anywhere after the ink has been applied toweb 12. For example, image processing apparatus 36 and camerapositioning unit 34 may be mounted between the last printing unit(either printing unit 14, 16, 18, and 20) and the oven, directly afterthe oven, on the chill rolls, or after the chill rolls. If opticaldensity measurements are required in the absence of other inks, or ifthe measurement is required immediately subsequent to printing, it maybe advantageous to mount image processing apparatus 36 and camerapositioning unit 34 between printing units 14, 16, 18, and 20.

Illumination system 38 may be in communication with computer 32 by asignal bus 52. Illumination system 38 may include a light source 42(only one shown) and a focusing mechanism 44. Control signals fromcomputer 32, corresponding to when a colorbar is within field of view56, may be sent via signal bus 52 to indicate when web 12 should beilluminated by light source 42. Light source 42 may be a xenon strobe,however other types of light sources may also be used. For example, forapplications with slower web speed, halogen bulbs may provideappropriate lighting.

In one embodiment, pulsed xenon strobe lights with a pulse duration ofapproximately one microsecond may be utilized. With a web speed of 3,500feet per minute and a limitation of moving the colorbar (or sampledregion) less than 0.003″ during the illumination period, a fivemicrosecond illumination time may be utilized to minimize the amount ofmovement of the printed image during the time image recording device 40is quantifying the amount of incoming light reflected from web 12. Byway of example, light source 42 may include a strobe light assemblyutilizing strobes FX-1163 with coordinated 1100 series power supplies,available from Perkin-Elmer.

Alternatively, a line array of LEDs may be used as light source 42 forilluminating a portion of web 12. In such a case, the LEDs may bearranged along the width of web 12 such that an optical distributor maynot be necessary. LEDs emitting white light may be employed, althoughother LEDs such as those emitting red, blue, or green light may be used,depending upon the sensors used and the type of image data required forthe application. The LEDs may provide the option of pulsed operation.

Light may be delivered to web 12 (directly or indirectly from lightsource 42) at an angle of approximately 45 degrees from the reflectedlight traveling to lens. The use of LEDs as light source 42 may requirethe use of reflectors to focus the emitted light in an advantageousmanner.

The illumination control signals from computer 32 may be produced, forexample, by conventional means utilizing rotational position informationgenerated from a sensor placed on one of blanket cylinders (22 or 26),knowledge of the speed of web 12, and knowledge of the distance betweenimage recording device 40 and one of blanket cylinders (22 or 26).

Focusing mechanism 44 efficiently concentrates the light emitted fromlight source 42 onto the image within field of view 56. When the strobelight is flashed, image recording device 40 may record the image withinfield of view 56, which contains portions of the colorbars. In someembodiments, to reduce the effects of scattered light, the lightingcould be modified such that only the colorbar is illuminated whenmeasuring the spectra.

In FIGS. 12A-12C, a process of detecting a colorbar 206 and focusinglight on colorbar 206 is shown, according to an exemplary embodiment. Inthis embodiment, web 12 may be moving in a direction 212 indicated bythe arrow. In FIG. 12A, as web 12 moves a first area 202 may beilluminated by light source 42 to determine whether colorbar 206 iswithin first area 202. In this exemplary embodiment, the system maydetermine that colorbar 206 was not within first area 202. The systemmay illuminate a second area 204 to determine whether colorbar 206 iswithin second area 204. In this exemplary embodiment, the system maydetermine that colorbar 206 was not within second area 204. In FIG. 12B,the system may illuminate a third area 208 to determine whether colorbar206 is within third area 208. In this exemplary embodiment, the systemmay determine that colorbar 206 was within third area 208. In FIG. 12C,based on determining that colorbar 206 was within third area 208, thesystem may focus the area of illumination to illuminate a fourth area210. Fourth area 210 may be a smaller area then first area 202, secondarea 204 and/or third area 208. Fourth area 210 may comprise the areaoccupied by colorbar 206, a portion of the area occupied by colorbar206, the area of colorbar 206 along with areas adjacent to colorbar 206,and/or a portion of the area occupied by colorbar 206 along with areasadjacent to colorbar 206. In one embodiment, a first camera (e.g., anRGB or other camera used for spatial processing) may be used to acquireimage areas 202, 204, and 208, and a second camera (e.g., aspectrophotometer or other camera used for color processing) may be usedto acquire image area 210.

Turning now to FIG. 3, image processing apparatus 36 is shown, accordingto an exemplary embodiment. Light may be reflected off of web 12 intoimage processing apparatus 36 and may be received by a beamsplitter 60.This reflected light may be the image acquired by image processingapparatus 36. Beamsplitters 60 of various reflection and transmissionpercentages may be used based on the overall efficiency of each path ofoptics. For example, if the spectral portion is less efficient than thespatial portion, beamsplitter 60 having a 30% reflectance and 70%transmittance may be used, where the transmitted portion of the beamprogresses along the spectral path.

The acquired image represents a thin slice through multiple patchesalong colorbar 206. Referring to FIG. 13, an illustration of acquiring aportion of multiple patches along colorbar 206 is shown, according to anexemplary embodiment. A portion of multiple colorbar patches 214 may bea part of colorbar 206, a share of colorbar 206, a slice of colorbar206, an area less than the whole area of colorbar 206, a segment ofcolorbar 206, a fragment of colorbar 206, etc. Portion of multiplecolorbar patches 214 may be a spectral measurement strip and portion ofmultiple colorbar patches 214 may be acquired by spectral imaging device74.

Colorbar 206 may comprises a colorbar length 220 and a colorbar width222. Colorbar width 222 may be at least 1.0 millimeters, at least 1.25millimeters, at least 1.56 millimeters, at least 1.75 millimeters, atleast 2.0 millimeters, or any other size. Colorbar length 220 may be atleast 10 millimeters, at least 20 millimeters, at least 25 millimeters,at least 30 millimeters, etc. Portion of multiple colorbar patches 214may comprises a portion length 216 and a portion width 218. Portionwidth 218 may be less than or equaled to 0.25 millimeters, less than orequaled to 0.35 millimeters, less than or equaled to 0.5 millimeters,less than or equaled to 0.9 millimeters, less than or equaled to 1.25millimeters, or any other size. Portion length 216 may be less than 10millimeters, less than 20 millimeters, less than 25 millimeters, lessthen 30 millimeters, or any other size. In an exemplary embodiment,colorbar width 222 is 1.56 millimeters and portion width 218 is 0.5millimeters. Spectral imaging device 74 may acquire spectralmeasurements from portion of multiple colorbar patches 214. Since thearea of portion of multiple colorbar patches 214 is less than the areaof colorbar 206, the spectral measurements received by spectral imagingdevice 74 is less (e.g., 32% less based on 0.5 millimeters divided by1.56 millimeters) than that of the total spectral measurements thatcould have been received from the entire colorbar 206.

In an exemplary embodiment, utilizing spatial imaging device 62 mayincrease the amount of spectral measurements that may be utilized (e.g.,to be utilized for color control or data reporting operations) in theprinting operation. Spatial imaging device 62 may acquire data from theentire colorbar 206. Since spatial imaging device 62 may acquire datafrom the entire colorbar 206, data points acquired by spatial imagingdevice 62 may be some of the same data points acquired by spectralimaging device 74. These common data points may be utilized tospectrally calibrate spatial imaging device 62 based on the spectralmeasurements acquired from these common data points by spectral imagingdevice 74. For example, spatial imaging device 62 acquires a measurementof X−1 for common point Z and spectral imaging device 74 acquires ameasurement of X for common point Z. In this example, spatial imagingdevice 62 measured a value of X−1 for common point Z and any other point(e.g., a point within the shared colorbar 206 area or a point withincolorbar 206 that is not shared between spectral imaging device 74 andspatial imaging device 62) that has a value of X−1 would be updated(e.g., modified, calibrated, etc.) to a value of X.

Spatial imaging device 62 may comprise, an RGB sensor, including forexample a three-chip RGB sensor or a single chip Bayer RGB sensor, anarea or line CCD sensor, a complementary metal-oxide-semiconductor(“CMOS”) sensor, or other type of sensor. In an exemplary embodiment,Bayer RGB sensor may comprises a filter pattern which is fifty percentgreen, twenty-five percent red, and twenty-five percent blue. Spatialimaging device 62 may further comprise other features such as lens, anillumination system, processing circuits, converter circuits, etc. andmay be used to create a camera or other imaging device. Spectral imagingdevice 74 may comprise a calorimeter, a spectral dispersion device suchas a spectrometer, prism, reflective grating, transmissive grating orthe like, or a spectrophotometer. One example of a spectral dispersiondevice is an ImSpector that is available from Spectral Imaging LTD,Oulu, Finland. The spectral imaging device 74 may further comprise otherfeatures such as a lens, an illumination system, processing circuits,converter circuits, etc. and may be used to create a camera or otherimaging device. An RGB camera may comprise three channels, each channelconfigured to sense light in a predetermined range of wavelengths (e.g.,red, green, and blue).

Spectral imaging device 74 may alternatively be a device that translatesincoming light into spectral measurements, which can be done at amultiplicity of spatial locations. A spectral measurement may be ameasurement of light at a multiplicity of wavelengths. The wavelengthscan be measured in at least five channels, at least eight channels, atleast twelve channels, at least twenty-four channels, at leastthirty-two channels, etc. In one embodiment, spectral imaging device 74may comprise a spectral dispersion device and a CCD sensor, such as ablack and white two-dimensional CCD sensor. In another embodiment,spectral imaging device 74 may comprise a spatial dispersion device tosplit incoming light into a multiplicity of beams. Each of these beamsof light may pass through one or more filters so as to pass a certainrange of wavelengths. The filtered beams of light may then be projectedonto a sensor (such as a linear CCD or other sensor) so that the lightmay be measured within that certain range of wavelengths.

In an exemplary embodiment, an RGB-based spatial imaging device 62 maybe used to image the entire colorbar patch and a fraction of the pixelsin the RGB spatial imaging device 62 have a corresponding measurementmade by spectral imaging device 74. This area where the images of boththe spatial and spectral imaging devices overlap may be used as acalibration area to calibrate the RGB pixels with respect to thespectral measurements. This calibration then may be extended to spatialimaging device's 62 other pixels that fall within the patch. Calibratingspatial imaging device 62 may be implemented by adjusting the averagedspectrum measured by spectral imaging device 74 by the differencemeasured between the pixels outside portion of multiple colorbar patches214 and the pixels inside portion of multiple colorbar patches 214. Thesystem may determine (e.g., calculates, predefines, etc.) that colorbar206 has a relatively consistent density and CIEL*a*b* (e.g., which is acolor space specified by the International Commission on Illumination)values. Since the system determines that colorbar 206 has relativelyconsistent density and CIEL*a*b* values, the system may need to adjustthe spectrum based on a difference between pixels measured withinportion of multiple colorbar patches 214 and the pixels measured outsideof portion of multiple colorbar patches 214. The adjustment to thespectrum may be implemented utilizing three color bands (e.g., red,blue, and green) measured by spatial imaging device 62. For example, ifthe pixels outside of portion of multiple colorbar patches 214 are morered, less blue and acceptable green, then the spectrum may be adjustedhigher on the red, adjusted lower on the blue and remain unchanged onthe green. In this example, the percentage of colorbar 206 utilized tocalculate the colorimetry (e.g., XYZ) and the density would increasefrom 32 percent to approximately 100 percent.

In FIG. 16, a flowchart of calibrating a spatial imaging device based oncalibration data from a spectral imaging device 500 is shown, accordingto an exemplary embodiment. Spatial imaging device 62 acquires datapoints from at least a portion of colorbar 206 area (step 502). Spectralimaging device 74 acquires data points from at least a portion ofcolorbar 206 area (step 504). The data points acquired by spatialimaging device 62 are compared to data points acquired by spectralimaging device 74 (step 506). A processor in spatial imaging device 62,spectral imaging device 74, and/or a separate processor determineswhether one data point from spatial imaging device 62 and spectralimaging device 74 are a shared data point (step 508). If there is noshared data point, then the process returns to step 502. If there is ashared data point, then the process moves to step 510. The processor inspatial imaging device 62, spectral imaging device 74, and/or theseparate processor calibrates spatial imaging device 62 based oncalibration data from spectral imaging device 74 (step 510).Alternatively, color data from spatial imaging device 62 may be used tocalibrate spectral imaging device 74 in a similar manner. In anotherembodiment, spatial data from spatial imaging device 62 may be used toregister spectral imaging device 74 in a similar manner.

In FIG. 17, a flowchart for controlling color in a printing operationand reporting out data including color space data and density data 600is shown, according to an exemplary embodiment. The color control andreporting system is initiated (step 602). The color control andreporting system acquires image data from web 12 or substrate (step604). The color control and reporting system determines density values(step 606). The color control and reporting system determines colorspace (e.g., CIE 1931 XYZ, Adobe RGB, sRGB, Adobe Wide Gamut RGB,CIEL*u*v*, CIEU*v*w*, CIEL*a*b*, etc.) values (step 608). The colorcontrol and reporting system determines whether density values are to bereported (step 610). If density values are to be reported, then thecolor control and reporting system transmits density values (step 612).The color control and reporting system determines whether color spacevalues are to be reported (step 614). If color space values are to bereported, then the color control and reporting system transmits colorspace values (step 616). The color control and reporting systemdetermines whether to control color based on color space values (step618). If color control is to be based on color space values, then thecolor control and reporting system controls color based on color spacevalues (step 620). For example, control signals may be provided to inkkeys of printing units for printing colors on the substrate. If colorcontrol is not to be based on color space values, then the color controland reporting system moves to step 622. The color control and reportingsystem determines whether to control color based on density values (step622). If color control is to be based on density values, then the colorcontrol and reporting system controls color based on density values(step 624). If color control is not to be based on density values, thenthe process moves back to step 604.

As illustrated in FIG. 3, a portion (i.e. a beam) of the acquired imageis diverted by beamsplitter 60 to a first imaging device. In theillustrated embodiment, the first imaging device is spatial imagingdevice 62. Spatial imaging device 62 may process the spatial informationfrom the acquired image. The spatial information conveys where on web 12the data is coming from.

Referring to FIG. 3, another portion of the same acquired image passesthrough beamsplitter 60 to the focusing lens L₁. From the lens L₁, theimage travels to an internal light blocker 66 having a slit 68 therein.Internal light blocker 66 is located inside of image recording device40. Internal light blocker 66 may be made of any material that preventslight from passing therethrough. In the illustrated embodiment, internallight blocker 66 is made of aluminum having a thickness of approximatelyten microns. Internal light blocker 66 may be darkened or black anodizedto reduce the incidence of reflected light off of internal light blocker66. The slit height and magnification of lens L₁ are chosen such that inthe vertical direction (the short dimension of colorbar 206),approximately one-half of the image of colorbar 206 is transmittedthrough slit 68. Internal light blocker 66 may allow for circumferentialmovement (i.e., how much the image “moves” from sample to sample) of+/−¼ of colorbar 206 height. The length of slit 68 may be chosen suchthat several colorbar 206 patches (i.e., at least two, at least four, atleast eight, at least ten, etc.) go through slit 68. The size of slit 68assures that only light from the reflected colorbar 206 passes throughslit 68, even if the image is not centered on slit 68. The lens L₁focuses the acquired image onto slit 68.

From slit 68, light travels to a collimating lens L₂. The lens L₂transmits light as a parallel beam to a ruled diffraction grating 72. Itis understood that a transmission-type diffraction grating may also beused. It is also understood that a prism 86 may be used instead ofdiffraction grating 72 as the dispersing element. A system utilizingprism 86 is described in more detail below with respect to FIG. 9.Diffraction grating 72 disperses light into its spectral componentsalong a known angular spread.

Diffraction gratings 72 may be designed to have higher efficiencies atparticular frequencies, but have non-zero efficiency over a very widerange. For example, part number F43-742 from Edmund Optics has 600lines/mm and is optimized to have maximum efficiency at 500 nanometers.However, this diffraction grating 72 has significant efficiency fromabout 300 nanometers to 1,200 nanometers. Light of multiple frequenciesmay also be diffracted at the same angle. For example, light at 800nanometers is first-order diffracted at the same angle as thesecond-order diffraction of 400 nanometers, and the third orderdiffraction of 267 nanometers. If overlapping spectra are not desired, acutoff filters 71 (FIG. 4) that block light of the wavelengths not ofinterest should be inserted in the optical path before diffractiongrating 72. In the illustrated embodiment, the system may be interestedin light between about 400 nanometers and about 700 nanometers such thatcutoff filters 71 may be inserted before diffraction grating 72 to blockall light above 700 nanometers and below 400 nanometers.

In the illustrated embodiment, the angular spread of light between about400 nanometers and 700 nanometers is approximately 12°. This dispersionoccurs in the vertical dimension (with reference to FIG. 5). A focusinglens L₃ focuses the dispersed light onto a second imaging device, whereit is captured. In the illustrated embodiment, the second imaging deviceis spectral imaging device 74. Spectral imaging device 74 may processthe spectral information from the acquired image.

FIG. 4 illustrates in more detail the optics of image processingapparatus 36 described above with respect to FIG. 3. As illustrated, theportion of the beam transmitted through beamsplitter 60 to the spatialcomponents travels through an aperture 76 (to help limit the amount ofincidental light and to help control the amount of aberrations) andthrough a lens L₄ onto spatial imaging device 62. The magnification ofthe spatial components may be such that the light fits across spatialimaging device 62. The lens L₄ may be placed such that spatial imagingdevice 62 is at the focal length f₄ of lens L₄.

In an exemplary embodiment, image processing apparatus 36 may include alens L₃, a lens L₄, aperture 76, spatial imaging device 62, spectralimaging device 74, and/or internal light blocker 66 inside of a housing.

The following process may be used to determine the proper opticalplacement of the spectral components (i.e. the proper focal lengths ofthe lenses, as well as the proper position of slit 68) within imagingprocessing apparatus 36 and to get the spectral spread to fit acrossspectral imaging device 74. In an exemplary embodiment, the processbegins at the end (i.e. spectral imaging device 74) and work back tocolorbar 206. First, the focal length f₃ of the lens L₃ is determined.This is dependent on the amount of spectral spread θ_(SS) off ofdiffraction grating 72. If spectral imaging device 74 has a heighth_(CCD), then tan(θ_(SS)/2)=h_(CCD)/2f₃. Thus, in order for the spectrato fit on the spectral CCD, f₃≦h_(CCD)/[2 tan(θ_(SS)/2)].

The spectral spread θ_(SS) is determined by the line spacing ofdiffraction grating 72, and the wavelengths of the light of interest. Inthe illustrated embodiment, diffraction grating 72 may be used which has600 lines/mm. The grating equation is mλ=d(sin θ_(m)−sin θ_(i)), wherem=the diffraction order, d=the groove spacing of diffraction grating 72,θ_(m)=the diffraction angle for order m, and θ_(i)=the incident angle ofthe light (e.g. the blaze angle, which is 8.6° in the illustratedembodiment).

For a blazed diffraction grating with blaze angle θ_(b), the diffractedlight efficiency is maximized when θ_(i)=θ_(b). If wavelengths fromλ₁=400 nanometers to λ₂=700 nanometers are of interest (whichapproximately covers the range of visible light), and d=1/600lines/mm=1,667 nanometers, then for the first order diffraction (whichmay be used because it has the highest strength of reflected light):

-   -   400 nanometers=1667 nanometers (sin θ_(m1)−sin(8.6°))    -   700 nanometers=1667 nanometers (sin θ_(m2)−sin(8.6°))    -   Therefore, θ_(m1)=22.9° and θ_(m2)=34.7°. Thus, the spectral        spread is θ_(ss)=34.7°-22.9° or θ_(ss)=11.8°.

Spectral imaging device 74 may be placed a distance from the lens L₃equal to the focal length f₃. In the spatial dimension, diffractiongrating 72 may act as a mirror.

If the slit height is h_(s)=0.1 mm, and 10 nanometers spectralresolution (or 36 bins) is desired, this equates to the zero-order slitwidth on spectral imaging device 74 having a height of h_(CCD)/36.Calculating spectral resolution based on the zero-order slit width is anapproximation, since the light through the slit has a non-uniformprofile. Thus, the lens L₃ and the lens L₂ need a combined magnificationof |M₂₃|≦h_(CCD)/[(0.1 mm)(36)]. |M₂₃|=f₃/f₂, where f₂ is the focallength of the lens L₂. Thus, f₃/f₂≦h_(CCD)/3.6 mm and f₂≧3.6 f₃/h_(CCD).

If the sampled height of the colorbar h_(sh) is to be magnified to theslit height h_(s), slit 68 may be placed at the image position s_(i) ofthe lens L₁ (to focus the image on slit 68) and at a distance equal tothe focal length f₂ of the lens L₂ (to collimate the light). Ifh_(sh)=0.8 mm (or approximately 1/32 inch), and h_(s)=0.1 mm, then thelens L₁ may be magnify by |M₁|=0.125. But, we also need the spatialdimension to fit across spatial imaging device 62.

Plugging in some values, let h_(CCD)=4.36 mm. Then f₃≦4.36 mm/[2 tan(11.8°/2)] and f₃≦18.0 mm. So, let f₃=14 mm. Then, f₂≧(3.6 mm)(14mm)/4.36 mm and f₂≧11.6 mm. If 25 mm is to spatially fit across spatialimaging device 62, the overall magnification |M₁₂₃| may be |M₁₂₃=4.36mm/25 mm and |M₁₂₃|=0.174. If |M₁|=0.125, then we need |M₁₂₃|≦1.39,f₃/f₂23 1.39, f₂≧(14 mm)/(1.39) and f₂≧10.1 mm.

The above calculations represent two constraints on the focal length f₂such that a focal length should be chosen that satisfies bothconstraints. So, let f₂=12.0 mm.

The image height h_(i) (i.e. the slit width) at the focal point of thelens L₂ may determine the spectral resolution in image processingapparatus 36. If 36 bins of spectral resolution are desired, then thelight incident on diffraction grating 72 may be within θ_(SS)/36 or13°/36=0.361°.

Finally, to calculate the focal length f₁ of the lens L₁, if|M₁|=f₁/x_(o)=0.125 (where x_(o) is a variable that equals the distancefrom the object to the focal point of the lens L₁) and x_(o)=100 mm,then f₁=12.5 mm. So we have f₁=12.5 mm, f₂=12.0 mm, and f₃=14.0 mm.

As described, image recording device 40 of the present disclosure mayinclude both spatial imaging device 62 and spectral imaging device 74.Image processing apparatus 36 as illustrated may process both thespatial and spectral information from the same acquired image (i.e.acquired from the same position on web 12 at the same time). The spatialand spectral images, taken together, allow the press operators toanalyze the print quality of the image and make adjustments, wherenecessary. This system allows for improved color control of printed web12 in that image processing apparatus 36 may measure the spectralresponse of colorbar patches within colorbar 206 with very fine spectralresolution. This makes it easier to match the densitometric andcalorimetric filters for measuring color to image processing apparatus36.

FIG. 5 illustrates the spectral and spatial information generated usingimage processing apparatus 36, according to an exemplary embodiment. Aspectral matrix 700 comprises a black column 710, a yellow column 712, amagenta column 714, and a cyan column 716 representing the spectralresponse of an image of a black color patch, a yellow color patch, amagenta color patch, and a cyan color patch. In an exemplary embodiment,black column 710 comprises an area which has a minimal spectral responsearea 702. In this exemplary embodiment, all or substantially all of thearea for black column 710 comprises minimal spectral response area 702.In an exemplary embodiment, yellow column 712 comprises at least fourareas. These four areas are minimal spectral response area 702, a highspectral response area 704, a medium spectral response area 706, and alow spectral response area 708. In an exemplary embodiment, magentacolumn 714 comprises at least three areas. These three areas are minimalspectral response area 702, medium spectral response area 706, and lowspectral response area 708. In an exemplary embodiment, cyan column 716comprises at least three areas. These three areas are minimal spectralresponse area 702, medium spectral response area 706, and low spectralresponse area 708. As illustrated, the spatial information may bemeasured along the horizontal axis and the spectral information alongthe vertical axis. Using this information, the print quality of theprinted substrate may be monitored and adjusted as necessary. Lighthaving a wavelength of approximately 400 nanometers may be located nearthe top of the image and light of approximately 700 nanometers may belocated near the bottom of the image.

In FIGS. 14A-14C, illustrations of a spatial imaging device 302 and aspectral imaging device 304 acquiring image data from a printed image342 are shown, according to exemplary embodiments. Spatial imagingdevice 302 may comprise a light reflector 306, internal light blocker66, a lens 308, and/or a first imaging unit 310 within a housing 303.First imaging unit 310 may process spatial data and/or spectral data.Referring to FIG. 15A, first imaging unit 310 may comprise a firstsensing element 362, a memory 366, a first processor 360, an interface364 and/or any combination thereof.

Spectral imaging device 304 may comprise light reflector 306, internallight blocker 66, lens 308, and/or a second imaging unit 312 in housing303. Second imaging unit 312 may process spatial data and/or spectraldata. Referring to FIG. 15B, second imaging unit 312 may comprise asecond sensing element 368, memory 366, a second processor 370,interface 364 and/or any combination thereof.

In an exemplary embodiment, spatial imaging device 302 may acquire afirst light 330 and a second light 332 from a colorbar area 324. A thirdlight 326 may not be acquired by spatial imaging device 302 becausethird light 326 may be blocked by a first external light blocker 316and/or a second external light blocker 314. First light 330 and secondlight 332 may be reflected off of reflector 306 to internal lightblocker 66. Internal light blocker 66 may block first light 330 andallow second light 332 to be transmitted to lens 308 based on spectralfrequency, scattered light criteria, lens 308 characteristics, firstimaging unit 310 characteristics, and/or any combination thereof. Lens308 focuses and/or collimates second light 332 into a fourth light 334which may be transmitted to first imaging unit 310. In alternativeembodiments, first light 330 and second light 332 are transmitteddirectly to internal light blocker 66, lens 308 and/or first imagingunit 310.

In an exemplary embodiment, spectral imaging device 304 may acquire afifth light 336 and a sixth light 338 from a portion of colorbar area322. A seventh light 328 may be blocked by a third external lightblocker 318 and/or a fourth external light blocker 320. Fifth light 336and sixth light 338 may be reflected off of reflector 306 to internallight blocker 66. Internal light blocker 66 may block fifth light 336and allow sixth light 338 to be transmitted to lens 308 based onspectral frequency, scattered light criteria, lens 308 characteristics,second imaging unit 312 characteristics, and/or any combination thereof.Lens 308 focuses and/or collimates sixth light 338 into a seventh light340 which may be transmitted to second imaging unit 312. In alternativeembodiments, fifth light 336 and sixth light 338 are transmitteddirectly to internal light blocker 66, lens 308 and/or second imagingunit 312. It should be noted that first external light blocker 316,second external light blocker 314, third external light blocker 318and/or a fourth external light blocker 320 may be positioned outside ofhousing 303.

In FIG. 14B, the system shown in FIG. 14A is illustrated with firstexternal light blocker 316, second external light blocker 314, thirdexternal light blocker 318, and fourth external light blocker 320positioned closer to spatial imaging device 302 and spectral imagingdevice 304, respectively. In FIG. 14C, the system shown in FIG. 14A isillustrated with the distance between first external light blocker 316and second external light blocker 314 increasing and the distancebetween third external light blocker 318 and fourth external lightblocker 320 increasing. It should be noted that the positions of firstexternal light blocker 316, second external light blocker 314, thirdexternal light blocker 318, and/or fourth external light blocker 320 maybe increased or decreased in relation to printed image 342, spectralimaging device 302, spatial imaging device 302, or each other.

Scattered light may be an issue in systems for measuring color qualitybecause scattered light affects the accuracy of the color measurement ofthe printed substrate. One solution to scattered light problems insystems for measuring color is described in U.S. Pat. No. 5,724,259, theentire contents of which is incorporated herein by reference. FIG. 6illustrates a flow chart of this scattered light correction process.Another solution to the scattered light issue may be to adjust theoptics and/or illumination of web 12 to reduce the effects of scatteredlight.

FIGS. 7 and 8 illustrate an alternative embodiment of the presentdisclosure utilizing separate spectral and spatial processors thatprocess separate acquired images. In this embodiment, both processorsmay be sampling a line around two inches long. With reference to FIG. 7,a spatial component 80 may include a single channel CCD positionedupstream from a spectral component 82. Spatial component 80 measures theposition on web 12 being measured to time the illumination of web 12,and thus the acquisition of the image, by spectral component 82 toensure that spectral component 82 is acquiring an image of the desiredregion of web 12. Spatial component 80 and spectral component 82 areconnected by a signal bus 84 such that spatial component 80 send asignal to spectral component 82 signaling spectral component 82 when toacquire an image from the printed substrate moving below imageprocessing apparatus 36. Utilizing the separate spatial and spectralimages may allow for the illumination of a very thin line acrosscolorbar 206 (or other region within the work), reducing any issuescaused by scattered light. Further, the scattered light that does remainis more easily correctable. A continuous light source 42 may be used toilluminate web 12 for spatial component 80, while a strobe may be usedto illuminate web 12 for spectral component 82.

In one embodiment, spatial component 80 may include a line-scan CCD thatmay continuously sample a line across web 12 in the lateral direction.In this design, the spatial resolution of spatial component 80 may be ofinterest. Circumferentially, this can be determined by the maximum linerate of the processor and the maximum press speed. For example, with apress moving at 3,000 ft/min, and if we want 0.0125″ per pixelcircumferentially, we need a line rate of 48 kHz. With 0.0125″resolution (or 80 dpi), and the smallest colorbar height being 1/16″,this provides for five pixels circumferentially, which should besufficient to locate colorbar 206. Laterally, the resolution isdetermined by the optics, the processor size, and the number of pixels.If we want to span two inches laterally, and the sensor has 128 pixels,we have a lateral resolution of 0.0156″, or 64 dpi. With a colorbarpatch width of 0.1″, this provides for 6.4 pixels per colorbar patch,which should be sufficient.

FIG. 8 illustrates the details of the optics design for spectral imagingdevice 74, according to an exemplary embodiment. The spectral optics aresimilar to those described above with respect to FIGS. 3 and 4, minusbeamsplitter 60, and thus will not be separately discussed.

FIG. 9 illustrates an alternative embodiment of the present disclosure.Prism 86 may be used to disperse the light in place of diffractiongrating 72, though it is understood that diffraction grating 72 may beused here in the same way as described above for FIG. 4. As mentionedabove, prism 86 may also replace diffraction grating 72 in theembodiments of FIG. 4 or 8. Depending on which dispersing element isused in the system, be it prism 86, diffraction grating 72, or otherdispersing element, there are different formulas to calculate theangular spread θ_(SS). Utilizing prism 86 results in an angular spreadθ_(SS) about one half as large as the angular spread θ_(SS) describedabove for FIG. 4. Using prism 86 results in a dispersion vs. wavelengththat is highly non-linear (prism 86 spreads the red wavelengths more andcompresses the blue wavelengths, resulting in lower resolution) and maybe corrected for. If the non-linearity of prism 86 is such that the bluewavelengths are compressed too much to obtain the desired spectralresolution, a smaller slit or a thinner line of illumination can beused. Using prism 86 as a dispersion element does not result in theoverlapping spectra described above with respect to diffraction grating72 of FIG. 4. Thus, no filters may be required before prism 86 to blockout unwanted light.

As illustrated in FIG. 9, a single spectral sensor 88 may be used tomonitor color quality. A thin line of web 12 is continuouslyilluminated. Spectral sensor 88 may measure the spectra of web 12continuously. Spectral sensor 88 may be utilized to build the spatialimage by applying a weighted transform that functionally convertsspectral sensor 88 to a monochrome sensor. The weighted transform is amathematical processing of the signal generated by spectral sensor 88.The application of the weighted transform allows spectral sensor 88 toalso extract the spatial information.

This embodiment may be used to control the color of printed web 12without utilizing colorbar 206 as spectral sensor 88 measures multiplelines across printed web 12 continuously, known in the art as marklesscolor control. The circumferential spatial resolution of imageprocessing apparatus 36 may then only be limited by the speed at whichspectral sensor 88 can scan web 12, and by the maximum press speed. Thespectral resolution, however, is independent of the press speed andspectral sensor 88 speed. Spectral sensor 88 may be a small formatarea-scan CCD with a fast frame rate that may continuously scan web 12.Spectral sensor 88 may receive an image similar to that shown in FIG. 5.The spectral optics of spectral sensor 88 may not require slit 68 whenthe area-scan CCD is used to achieve the desired spectral resolutionbecause only a thin line of web 12 is illuminated. However, slit 68 maystill be used and may be desirable to ensure that the desired spectralresolution is accomplished. The slit width, or line width where slit 68is not used, determines the spectral resolution. The spectral optics ofthis embodiment are very similar to those discussed above with respectto FIG. 4, and thus will not be separately discussed. It is understoodthat in other embodiments (not shown), spectral sensor 88 may be aline-scan CCD.

In another aspect of the disclosure as shown in FIGS. 10 and 11, imageprocessing apparatus 36 may include a first processor and a secondprocessor. Both the first and second processors are capable ofprocessing the spectral information from an acquired image and neitherof the first or second processors may necessarily be dedicated toprocessing the spatial or spectral information from the acquired image.When it is said that both processors are capable of processing thespectral information, it is meant that both processors are capable ofproviding measurements to a control feedback loop or to the pressoperator in a certain color space and/or color space format.

A color space comprises a color model and a reference color space. Toobtain a color space, the color model (e.g., RGB and CMYK are colormodels) may be added to a mapping function between the color model and acertain reference color space results in a definite footprint or gamut.When the footprint or gamut is combined with the color model a colorspace is defined (e.g., Adobe RGB and sRGB are two different absolutecolor spaces, both based on the RGB model). Color spaces may be CIE 1931XYZ, Adobe RGB, sRGB, Adobe Wide Gamut RGB, CIEL*u*v*, CIEU*v*w*,CIEL*a*b*, CIEL*c*h*, DIN99, etc.

Color space conversion may be the translation of the representation of acolor from one color space basis to another color space basis. This mayoccur in the context of converting an image that is represented in onecolor space to another color space, the goal being to make thetranslated image look as similar as possible to the original.

Referring to FIGS. 10 and 11, one of the first processor and secondprocessor may comprise a large format sensor (e.g. it is capable ofmeasuring a large number of pixels of information) and the otherprocessor may comprise a small format sensor (e.g. it may be capable ofmeasuring a smaller number of pixels or even a single pixel). In anexemplary embodiment, a small format sensor may be a sensor that whenused in combination with a second sensor (e.g. a large format sensor)measures less pixels then the second sensor. In another exemplaryembodiment, a small format sensor may be a sensor that when used incombination with a second sensor (e.g. a large format sensor) measuresreflectance units or any other color measurement data more accuratelythan the second sensor. The small format sensor may be a spot sensor,with at least three channels (e.g., a calorimeter), or a 1×N line scansensor, where N is the number of spectral bins, and some spectraldispersion element spreads the spectra of the spot along the longdimension of the sensor. The small format sensor may be a 2-D sensor ina hyperspectral imaging device configuration. In another exemplaryembodiment, two large format sensors may be utilized. The first largeformat sensor may be configured to analyze the data utilizing a largerprocessing time than the second large format sensor. The large formatsensor may be any size and could be either an area scan or a line scansensor. The large format sensor may be an RGB area sensor (e.g., around256×256 pixels). The RGB to CMYK or RGB to L*a*b* color transforms maybe adjusted based on data read from the small format sensor. The colormeasurement of the acquired image may be implemented using a smallformat sensor that measures only a single spot of color. However, thismay make the color measurement process too slow to be practical for usein web printing applications. The combination of the large format sensorand small format sensor in image processing apparatus 36 may be acompromise of high resolution color measurement and speed. Further, byworking together, both the small format sensor and the large formatsensor may provide color information in different color spaces, eventhough the large format sensor may be gray scale, by a calibrationalgorithm. Based on several measurement comparisons, the large formatsensor may be calibrated to the small format sensor by the calculationof slope and offset correction constants. The calculation of differenttypes of correction constants may be possible, for example, with aquadratic correction constant.

Specifically with respect to the idea of calibrating one sensor to theother, a couple of examples follow. Assuming that the small formatsensor has an accurate response over its full dynamic range (i.e., anynon-linearities are removed by using data from a calibration procedure),and assuming that both sensors have the same spectral resolution, thenthe small format sensor measures an area included in a larger areameasured by the large format sensor. For some spectral channel, thelarge format sensor may report this small area to read 0.25 reflectanceunits and the small format sensor may report 0.20 reflectance units forthis small area. For another spot, the large format sensor may report0.85 reflectance units, and the small format sensor may report 0.83reflectance units. Similar data is collected for many such spots. Somecorrection is applied to the large format sensor data to make thesereadings agree in an optimal sense. A simple linear correction:R_(L)=a₁*R_(S)+a₂ may be assumed, where R_(L) is the response of thelarge format sensor, R_(S) the response of the small format sensor, anda₁ and a₂ are constants determined by fitting responses of the sensorsto this model. The more data collected and the more the data spans thedynamic ranges of the two sensors, the better the calibration.

However, if it is assumed that the sensors have different spectralresolution, then the spectral response of the low spectral resolutionsensor may be approximated with spectral data from the high spectralresolution sensor. Assuming one channel (such as red) of the lowspectral resolution sensor has a given spectral response, which may beestimated based upon manufacturer's data, and assuming there is anestimate of the low spectral resolution sensor spectral response in 20nanometers intervals, then the high spectral resolution sensor mightmeasure at 5 nanometers resolution. The manufacturer's data may beinterpolated to obtain 5 nanometers spectral data. Then, a broadbandwidth filter is applied to the high spectral resolution sensor datato approximate what the low spectral resolution sensor may see in thered channel. Now, one sensor can be fit to the other as described in theprevious paragraph.

The small format sensor may be removed from image processing apparatus36 and image processing apparatus 36 may still perform its functions,though the color measurement will be at a lower resolution. This allowsfor accurate off-line calibration of the small sensor without a stoppageof the equipment being necessary. This increases the efficiency of thesystem in that image processing can still take place when calibration ofthe small format sensor is necessary (i.e., when the small format sensoris not functioning) and also increases the repeatability of measurementsbetween the color desk sensor and the on-line sensor. The removablesmall format sensor can be installed into a desktop color measurementdevice, which will allow for direct comparison (and hence, calibration)of color measurements between the on-press and off-press devices. Italso may allow current systems that utilize only the large format to beupgraded by the addition of the small format sensor.

Referring to FIG. 10, the first processor is a large format sensor, suchas a single black and white CCD sensor 100, according to an exemplaryembodiment. One such sensor 100 that may be used is model numberKAF-0261E, available from Kodak. In general, sensor 100 may process thespatial information from the acquired image, however, it is understoodthat sensor 100 may be capable of processing the spectral information aswell. Generally, sensor 100 has low spectral resolution to increase theprocessing speed of image processing apparatus 36. Many of the detailsof the optics in FIG. 10 and their proper placement and/or alignment areexplained in detail above with respect to FIG. 4 and therefore will notbe discussed here.

The second processor is a small format sensor, such as a line-scan CCDsensor 104. Line-scan CCD sensors 104 may be model number IL-P3-0512available from Dalsa Corporation of Waterloo, Ontario Canada, or modelnumber CCD39-02, available from e2v technologies of Elmsford, N.Y.Line-scan CCD sensor 104 may measure a point of color and has a highspectral resolution. Line-scan CCD sensor 104 may process the spectralinformation from the acquired image. As illustrated in FIG. 10, a fiberoptic bundle 108 receives at least a portion of the acquired image fromslit 68 and transports that portion of the image to the collimating lensL₂. Fiber optic bundle 108 may receive 100% of a first portion of thelight reflected from web 12. The remaining portion (a second portion ofthe reflected light) of the acquired image may then be directed toline-scan CCD sensor 104. It is understood by one of skill in the artthat beamsplitter 60 may be used in addition to fiber optic bundle 108to deliver the image to the lens L₂ such that the fields of view ofsensor 100 and line-scan CCD sensor 104 overlap. It is also understoodthat a mirror may be used in place of fiber optic bundle 108.

The lens L₂ transmits light as a parallel beam to the ruled diffractiongrating 72. It is understood that a transmission-type diffractiongrating 72 or prism 86 may be used instead of diffraction grating 72 asthe dispersion element. It is also understood that a color filter wheelor other changeable color filters may be used instead of diffractiongrating 72 or prism 86. Diffraction grating 72 disperses light into itsspectral components along a known angular spread. The focusing lens L₃focuses the dispersed light onto line-scan CCD sensor 104.

Sensor 100 and line-scan CCD sensor 104 may be in communication witheach other (with reference to FIG. 7) such that information generated byone sensor may be used to direct the function of the other. For example,sensor 100 may take a picture of the printed substrate that includes thearea to be analyzed. This information may be used to register line-scanCCD sensor 104 in that the information obtained from sensor 100 directsline-scan CCD sensor 104 when to snap its picture to ensure thatline-scan CCD sensor 104, which takes a much smaller picture than sensor100, gets an image of the appropriate area.

In return, line-scan CCD sensor 104, which has a higher resolution andmeasures a much smaller area, may be used to calibrate sensor 100. Forexample, because line-scan CCD sensor 104 acquires an image in lesslight, line-scan CCD sensor 104 may be less affected by scattered light.By comparing the measurements from line-scan CCD sensor 104 with sensor100, which takes in a greater amount of light and thus is more affectedby scattered light, sensor 100 may be adjusted to remove theinaccuracies caused by the scattered light based upon the more accuratemeasurement from line-scan CCD sensor 104. Other measurementinaccuracies, such as non-linearity problems, may also be calibrated outby comparing readings between sensor 100 and line-scan CCD sensor 104.

FIG. 11 illustrates an alternative embodiment of the disclosure. Ingeneral, the first processor may process the spatial information from anacquired image of the printed substrate and the second processor mayprocess the spectral information, though it is understood that both thefirst and second processors may be capable of processing spectralinformation from an acquired image, as is defined above.

The first processor may include a large format sensor, such as a threeCCD, RGB color sensor 112. RGB color sensor 112 may include a dichroicprism 116 and a three CCD array including a red color filter 120, agreen color filter 124, and a blue color filter 128. Red color filter120 may transmit the red light and reflects blue and green light backinto dichroic prism 116. Similarly, green color filter 124 may transmitgreen light, and blue color filter 128 may transmit blue light. In thisway, none of the light transmitted into dichroic prism 116 is lost.

The image processing device of FIG. 11 utilizes the RGB color sensor 112as the first processor, and a small format sensor, such as an area-scanCCD sensor 132, as the second processor. Area-scan CCD sensor 132 mayhave a high spectral resolution and may measure a line of color acrossthe printed substrate. Generally, area-scan CCD sensor 132 may have agreater spectral resolution than, but will also be much slower than, RGBcolor sensor 112.

In the embodiment of FIG. 11, RGB color sensor 112 and area-scan CCDsensor 132 may analyze an acquired image. As illustrated, beamsplitter60 reflects a portion of the acquired image from the printed substrateand directs the acquired image to RGB color sensor 112. For example, ifbeamsplitter 60 has a reflectance of fifty percent, fifty percent of thereflected light is directed to RGB color sensor 112. The other fiftypercent is directed to area scan CCD sensor 132 and thus area-scan CCD132 sees the same acquired image. Overall, the specific optics designfor area-scan CCD sensor 132 may be similar to those described abovewith respect to FIG. 4 and thus will not be described again here. In anexemplary embodiment, a line-scan sensor may obtain image data from aregion (e.g., a line) which has a width of one pixel and a length ofmultiple pixels. In another exemplary embodiment, an area-scan sensormay obtain image data from a region which has a width of more than onepixel and a length of more than one pixel.

Although the description contains many specifics, these specifics areutilized to illustrate some of the exemplary embodiments of thisdisclosure and should not be construed as limiting the scope of thedisclosure. The scope of this disclosure should be determined by theclaims, their legal equivalents and the fact that it fully encompassesother embodiments which may become apparent to those skilled in the art.All structural, chemical, and functional equivalents to the elements ofthe below-described disclosure that are known to those of ordinary skillin the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. A reference to anelement in the singular is not intended to mean one and only one, unlessexplicitly so stated, but rather it should be construed to mean at leastone. No claim element herein is to be construed under the provisions of35 U.S.C. §112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for.” Furthermore, no element, component ormethod step in the present disclosure is intended to be dedicated to thepublic, regardless of whether the element, component or method step isexplicitly recited in the claims. It is to be understood that thedisclosure is not limited in its application to the details ofconstruction and the arrangement of components set forth in thedescription or illustrated in the drawings. The disclosure is capable ofother embodiments and of being practiced in various ways. Also, it is tobe understood that the phraseology used herein is for the purpose ofdescription and should not be regarded as limiting. It should be notedthat module, system, or apparatus may refer to a functional unit relatedto a method, a device, software, or any combination thereof, any may beoperable or found in one or more pieces or software, or be a combinationof software and non-software systems. Use of the term module, system, orapparatus herein may refer to either computer program and/or circuitcomponents operating the computer program (e.g., one or more computers,servers, etc.) to carry out the functions described herein, eitherautomatically without user input or under control of a user. Module,system, or apparatus may interface with other modules, systems, orapparatuses at a hardware and/or computer program level, and may operateat and/or interface with other modules, systems, or apparatuses at anyapplicable computer program level specified in the Open SystemsInterconnection (OSI) model, such as application layer, presentationlayer, session layer, transport layer, network layer, data link,physical layer, etc. Modules, systems, or apparatuses may be representedby a block, multiple blocks or portions of blocks in the various figuresherein.

What is claimed is:
 1. An image processing apparatus for use with aprinted substrate, the image processing apparatus comprising: a firstimaging device configured to receive light reflected from a portion ofmultiple patches of a colorbar on the printed substrate and configuredto process color data from the light reflected from the portion ofmultiple patches of the colorbar; and a second imaging device configuredto receive light reflected from the printed substrate and configured toprocess spatial information from the light, wherein the first imagingdevice is configured to acquire a first image of a portion of theprinted substrate and is configured to process the color data from thefirst image using a first processing circuit of the first imagingdevice, wherein the second imaging device is configured to acquire asecond image, wherein the second image comprises the first imageacquired from the same portion of the printed substrate at the same timeas the first imaging device, and wherein the second imaging device isconfigured to process spatial information from the second image using aseparate second processing circuit of the second imaging device.
 2. Theimage processing apparatus of claim 1, wherein the portion of multiplepatches of the colorbar is a slice of multiple patches of the color. 3.The image processing apparatus of claim 1, wherein the first imagingdevice comprises a line-scan sensor.
 4. The image processing apparatusof claim 1, wherein the second imaging device comprises an area-scan CCDsensor.
 5. The image processing apparatus of claim 1, wherein the secondimaging device is coupled to a fiber optic bundle to capture and directthe light reflected from the printed substrate to the second imagingdevice.
 6. The image processing apparatus of claim 1, wherein the firstimaging device has a higher spectral resolution than the second imagingdevice.
 7. The image processing apparatus of claim 1, wherein the firstimaging device acquires an image based on a signal from the secondimaging device.
 8. The image processing apparatus of claim 1, whereinthe spatial information from the second imaging device is used tocontrol registration of the first imaging device.
 9. The imageprocessing apparatus of claim 1, wherein the color data from the firstimaging device is used to calibrate the second imaging device.
 10. Theimage processing apparatus of claim 1, wherein a first dynamic sensorrange of the first imaging device and a second dynamic sensor range ofthe second imaging device are different.
 11. The image processingapparatus of claim 1, further comprising an illuminator, the illuminatorconfigured to illuminate a first area based on a first control signaland to illuminate a second area based on a second control signal;wherein the second control signal is based on locating the colorbar; andwherein the second area is smaller than the first area.
 12. The imageprocessing apparatus of claim 1, wherein the portion of multiple patchesof the colorbar is a thin slice of multiple patches of the colorbar. 13.The image processing apparatus of claim 1, wherein the first imagingdevice comprises a colorimetric filter.
 14. The image processingapparatus of claim 1, wherein the first imaging device comprises amonochrome sensor.
 15. The image processing apparatus of claim 1,wherein the first imaging device comprises a three-color CCD sensor. 16.An image processing apparatus for use with a printed substrate, theimage processing apparatus comprising: a first imaging device configuredto receive light reflected from a slice of multiple patches of acolorbar on the printed substrate and configured to process color datafrom the light reflected from the slice of multiple patches of thecolorbar; and a second imaging device configured to receive lightreflected from the printed substrate and configured to process spatialinformation from the light, wherein the first imaging device isconfigured to acquire a first image of a portion of the printedsubstrate and is configured to process the color data from the firstimage using a first processing circuit of the first imaging device,wherein the second imaging device is configured to acquire a secondimage, wherein the second image comprises the first image acquired fromthe same portion of the printed substrate at the same time as the firstimaging device, and wherein the second imaging device is configured toprocess spatial information from the second image using a separatesecond processing circuit of the second imaging device.
 17. The imageprocessing apparatus of claim 16, wherein the color data from the firstimaging device is used to calibrate the second imaging device.
 18. Theimage processing apparatus of claim 17, further comprising anilluminator, the illuminator configured to illuminate a first area basedon a first control signal and to illuminate a second area based on asecond control signal; wherein the second control signal is based onlocating the colorbar; and wherein the second area is smaller than thefirst area.
 19. The image processing apparatus of claim 1, furthercomprising a housing in which both the first imaging device and thesecond imaging device are positioned, wherein the first imaging deviceand the second imaging device are positioned in the housing in such amanner that the first imaging device and the second imaging device aredirected at the same portion of the printed substrate.